The present invention relates generally to apparatus for installing blind rivets and, more specifically, to an attachment adapted to automatically feed and install blind rivets when attached to an existing rivet installation machine.
A pull-type blind rivet is a well-known fastener. Although the rivets of various manufacturers may differ in some respects, all pull-type blind rivets comprise a substantially cylindrical stem, an enlarged head portion frangibly connected to one end of the stem, and a shank portion connected to the head. Some rivets additionally have a locking ring anvil collar around the stem in contact with the head.
To join workpieces using such a rivet, the rivet stem is inserted into the chuck or nose of the rivet installation tool, which firmly grasps the rivet stem. The rivet shank is then inserted into a hole through the workpieces and the rivet installation tool, restraining the rivet head against motion relative to the workpieces, applies a pulling force to the stem such that the head engages the head, thereby upsetting it and forming an enlarged mushroom-shaped head on the "blind" side of the workpieces. The stem is then broken off by further pulling and is discarded.
Both portable, hand-held riveting machines and permanently mounted riveting machines suitable for production-line assembly are known. However, because of the complexity of the problems involved in automatically feeding blind rivets from a bulk supply, operators of riveting machines known in the art have been required to manually insert each rivet stem into the nose of the pulling head and to manually eject the broken-off rivet stem from the nose after the riveting operation was complete.
Practitioners in the art have solved some of the problems involved in developing devices for automatically feeding pull-type blind rivets to riveting tools. U.S. Pat. No. 4,604,889 issued to Sukharevsky discloses a hand-held riveting tool with a cam-operated pivoting arm that feeds rivets into the nose portion of the riveting tool. The arm, which is disposed substantially parallel to the direction of pulling force, catches the stem of a rivet pneumatically ejected from a supply tube and pivots to a position such that the rivet stem is aligned with the nose. A hydraulic piston and valve assembly advances the nose to engage the rivet stem, at which point the arm pivots away. After the riveting operation is completed, the broken-off stem is pneumatically drawn into the installation tool and ejected rearward.
U.S. Pat. No. 4,747,294 issued to Schwartz et al. discloses a device for feeding rivets to a rivet installation tool. Unlike Sukharevsky, Schwartz et al. slidably mount a hand-held rivet installation tool on rails that are fixed relative to the workpiece. A rivet transfer arm, which is rotatably mounted perpendicular to the direction of pulling force, slides axially relative to the rails. The transfer arm catches the stem of a rivet pneumatically ejected from a supply tube. It then slides axially away from the feed tube and rotates to a position such that the rivet stem is aligned with the nose. The rivet is ejected from the transfer arm by pneumatic force and is received stem-first by the nose. The transfer arm then rotates away and the tool is advanced along the rails toward the workpiece and the riveting is performed. The broken-off stem is ejected rearwards through the installation tool. Schwartz alternatively discloses advancing and rotating the transfer arm while the installation tool remains fixed.
Neither Sukharevsky nor Schwartz et al. address the problem of fitting an existing rivet installation system with an automatic rivet feeding attachment. Many manufacturers use a general-purpose fastener installation machine that is suited for various fastener types. These machines typically have a reciprocating shuttle on which the fastener tool of choice and a drill mounted are mounted. The shuttle alternately moves the fastener tool and the drill to a position above the workpiece where a fastener can be installed. The shuttle can be positioned with extreme accuracy. The GEMCOR G-400B, produced by the General Drivmatic Co., is an example of such a machine. A blind rivet installation tool such as the Cherry-Textron Model AF704-39 can be mounted on the G-400B fastener installation machine shuttle. However, the lack of a suitable automatic blind rivet feeding system for such systems has forced manufacturers to manually feed rivets to the machine and then manually eject the broken-off stems.
It is not economical for manufacturers already having a blind rivet installation system such as that described above to purchase completely new equipment that is not otherwise as suitable for the sole purpose of acquiring automatic rivet feeding capability. The rivet installation system described above is often more flexible and more suited to manufacturers, needs on production lines than the tools described by Sukharevsky and Schwartz et al.
Furthermore, prior automatic rivet feeding systems have required a separate pneumatic or hydraulic power source apart from that used by the installation tool to supply the rivet pulling force. The need to synchronize the operation of these sources with the operation of the rivet installation tool itself has created the need for complex control systems that involve a large number of sensors.
An automatic blind rivet feeding system that is easily attached to existing fastener installation machines, requires a minimum of external power and control connections, and is easily synchronized with the existing operation of the installation tool would be desirable. These problems and deficiencies are clearly felt in the art and are solved by the present invention in the manner described below.